Common Names

Mahoe whitefly

Taxonomic Notes

The definition of whitefly species is usually based on details of the structure of the puparium, the fully grown fourth instar larva that holds the whitefly pupa. One key feature of the puparium of the Mahoe whitefly, Asterochiton aureus is the presence of four bands of pores on the disc and pores near the margin of the puparium.

There have been no studies of the annual cycle of the Mahoe whitefly. In Auckland there appear to be over lapping generations with a major period of egg laying associated with new leaves in the spring. Mahoe whitefly has the same life stages and life cycle as the greenhouse whitefly, Trialeurodes vaporariorum.

The adult whitefly is about 2 mm long and has a wing-span of about 3 mm. When the adults emerge, the pale cream body colour can be seen and the wings are transparent, but soon the body and wings become covered with white wax. There are males and females in this species. Males may be seen sitting alongside females before mating. Like most adult insects, they have three pairs of legs and two pairs of wings. The head has a pair of black compound eyes and pale antennae. Like other Hemiptera, the underside of the head has a rostrum that holds the long stylets used for feeding. Feeding is mainly on the underside of leaves. When feeding the adult appears to rotate around the place where the stylets are inserted. This create a circular patch of white wax on the underside of the leaf.

Adult females lay eggs on the underside of the leaf, often in circles around where they are feeding. The pale, oval eggs are laid on their sides but may have a peg at one end that is inserted into the leaf. The first larva to hatch from the egg has three pairs of legs and is usually called a crawler. It walks away from the egg and settles at a suitable feeding site, usually above or close to a leaf vein with phloem ducts (tubes that transmit nutrients from the leaf to other parts of the plant). The crawler is oval, flat and transparent. There are four larval instars (stages). The larvae grow by moulting, (i.e. changing skin). The old skin splits on the upper dorsal side and is pushed off the rear end of the new larva which stays and feeds in the same place.

The fourth instar larva is initially transparent like the earlier instars, but as it grows the background colour becomes a pale cream to pale brown and the central area becomes mid brown to black. When it is reaches full size, it pupates inside the larval skin, which is now called a puparium. The dark central colouration appears to cover the underlying pupa. When the adult is almost ready to emerge, a T-shaped split occurs in the skin of the puparium and the adult pulls itself out. Its wings expand and harden, and the body and wings become covered in white wax.

Feeding and honeydewWhitefly adults and larvae have sucking mouthparts. Long specially shaped rods called stylets are held in the sheath-like rostrum. When it wishes to feed, the whitefly moves the tip of the rostrum onto the surface of the plant leaf. The stylets are then gradually pushed into the plant and manoeuvred into the phloem (or nutrient transport vessels) of the plant. The whiteflies suck the plant’s sap, which is high in sugars and low in other nutrients. Whiteflies excrete the excess sugary liquid, which is called honey-dew. In the larvae, the excess liquid is excreted into a structure called the vasiform orifice where it accumulates. When a droplet has formed, a tongue-like structure called the lingula flicks the droplet away from the larva. It can be flicked up to 2 cm away.

Recognition

In New Zealand, Mahoe whitefly is one of two species of whitefly found on shrubs and tree of Melicytus species (Violaceae). The other species is Melicytus whitefly, Bemisia flocculosa Gill & Holder, 2011, that has been found on large and small leaved Melicytus species in the South Island. While specialist knowledge is required to distinguish the adults, the larvae and puparia of each species are easy to recognise.

The larvae of Mahoe whitefly are transparent and the puparia have a dark pigment running the length of the body. There is no white wax coating or any wax rods.

The larvae Melicytus whitefly are pale or tan coloured, while the puparia are tan coloured and are often partly coated with white wax. They also have a short fringe of wax rods.

Natural Enemies

No fungal pathogens, parasitoids and predators of the mahoe whitefly have been recorded. However, two fungal pathogens, pink and black, have been seen on the larvae and puparia, and one puparium was found that contained the pupa of a wasp (Hymenoptera) parasitoid. It is also likely that spiders and other generalist insect predators feed on whiteflies.

Host Plants

The Mahoe whitefly has only been found on two large leaved species of Melicytus. It may be present on other large leaved species in the genus.

Feeding and honeydewWhitefly adults and larvae have sucking mouthparts. Long specially shaped rods called stylets are held in the sheath-like rostrum. When it wishes to feed, the whitefly moves the tip of the rostrum onto the surface of the plant leaf. The stylets are then gradually pushed into the plant and manoeuvred into the phloem (or nutrient transport vessels) of the plant. The whiteflies suck the plant’s sap, which is high in sugars and low in other nutrients. Whiteflies excrete the excess sugary liquid, which is called honeydew. Honeydew makes the plant leaves sticky. Sometimes black sooty mould fungi grow on the sticky surfaces.